The present invention is directed toward lifting tongs for use with a crane and more particularly toward such lifting tongs which are specifically adapted to lift I-beams and similar materials of different sizes.
Various lifting tongs for lifting I-beams and the like have been proposed in the past. These are shown, for example, in U.S. Pat. Nos. 3,201,167 and 3,572,808. In each of these patents, the tongs include jaws which fit around the edges of the top flange of the I-beam. While these devices would appear to have some value for a particular size I-beam, they cannot safely be used with different size I-beams having different widths or thicknesses.
In co-pending application Ser. No. 339,108, filed Jan. 13, 1982, Applicant describes lifting tongs which have adjustable and interchangeable jaws so that the same can be used to lift I-beams of various different sizes. While the device shown in this prior application has many advantages over the prior art as described in said application, it does have certain limitations. The most significant of these is the fact that two people are required to operate the device. That is, a worker is needed to align the jaws with the flange on the I-beam as the jaws are being closed therearound. This not only results in a potentially dangerous situation for the worker but also adds considerable expense to the cost of operating the equipment.